Broadcast antenna



March 28, 1950 N. E. LINDENBLAD I 2,501,778

BROADCAST ANTENNA 5 Filed Oct. 10, 1946 rmkwrma INVENTOR ATTORNEYPatented Mar. 28, 1950 atoms BROABCAST ANTENNA Nils E. Lindenblad, PortJefferson, N. Y., assignor to Radio Corporation of America, acorporation of Delaware Application October 10, 1946, Serial No. 702,426

7 Claims. 1

The present invention relates to broadcast antennas and moreparticularly to non-resonant broadcast antennas which may be used over awide band of frequencies without discrimination.

An object of the present invention is to provide a broadcast antennawhich is non-resonant. Another object of the present invention is theprovision of an antenna which provides a large amount of low angleradiation for broadcast'purposes without the use of highantennastructures.

Another object of the present invention is the provision of an antennawhich may be efiiciently operated at a poor location having ahighresistance ground. v

The foregoing objects and others which may appear from the followingdetailed description are attained in accordance with the principles ofthe present invention by providing an antenna in the form of a conductordisposed about the circumference of a circle having a diameter of theorder of several wavelengths and fed with travelling waves. Thecircularly arranged conductor is spaced a short distance above a poorlyconducting ground surface. The conductor is therefore eiiectivelylocated at one side of a boundary between two dielectrics. Theunderlying dielectric, the ground, has such relative characteristicsthat it provides a distorted image. The cancelling effect between thewire and the image is reduced to a high degree at low angles in thedirection of the wire and away from the boundary and the image producingdielectric providing a resultant radiation in these directions. Themajor portion of the radiation from such an antenna is verticallypolarized.

The present invention will be more fully understood by reference to thefollowing detailed description which is accompanied by a drawing, not toscale, in which:

Figure 1 illustrates in perspective an embodiment of the presentinvention, while Figure 2 illustrates a modification thereof.

Referring now to Figure 1 there is shown a number of supporting polesIll arranged around the circumference of a circle having a diameter ofthe order of several wavelengths at the frequency with which the antennais to be operated. The poles support conductor M through theintermediary of insulators l2. The ring conductor it being supported ina generally circular configuration acts as the radiator. It is fed atone end by transmitter l6 and is terminated at the other end byterminating resistor IS. The terminating resistor I8 has such value ofresistance as to match the surge impedance of the line 14.

2 Thus, a pure travelling wave is set up along the conductor M whentransmitter I6 is energized.

Since the ground over which the antenna is arranged is a high resistanceground, the image of wire [4 produced in the high resistance groundis'distorted The cancelling effect takingplace over aground of highconductivity between the wire l4 and its closely adjacent image isespecially' reduced at the lower angles in the direction of the wiredue-to this distortion of the image. Thus, the major portion of theenergy is radiated in a direction approaching the direction of theantenna wire and is therefore vertically polarized. Due to the circulararrangement of the wire it is radiated tangentially and uniformly in alldirections and, of course, at a comparatively low, upward angle withrespect to the ground as a result of the distorted image.

For operation. in the present broadcast band, for example, the antennamight have a diameter of the'order of a thousand feet and be'separatedby poles 15 or ZO-feet high. It is only necessary that the poles be highenough to provide clearance for any trafiic which may have to'pass underthe wires.

The modification shown in Figure 2 differs from that in Figure 1 only inthat a pair of wires 24 and 26 are used. The wires are fed fromtransmitter 16 at the oposite ends of the diameter of the circle and areterminated by terminating resistors 28 and 33 respectively. Conductors24 and 26 each occupy a semi-circumference of the entire circle and arefed in an inphase relationship at opposite ends of a diameter of thecircle. The radiation from the antenna of Figure 2 takes place in thesame way as described above with reference to Figure 1.

While I have illustrated a particular embodiment of the presentinvention, it should be clearly understood that it is not limitedthereto since many modifications may be made in the several elementsemployed and in their arrangement without departing from the spirit andscope of the invention.

What is claimed is:

1. A broadcast antenna for vertically polarized radiation at low angleswith respect to ground comprising a number of conductors arranged in anend-to-end relationship to form a substantially closed geometricalfigure having a transverse dimension greater than several operatingwavelengths, said conductors being spaced a short distance above apoorly conductive ground, means connected to one end of each of saidconductors for energizing said conductors with a travelling wave andreflection preventing means connected between the other end of eachconductor and ground.

2. A broadcast antenna for vertically polarized radiation at low angleswith respect to ground comprising a number of conductors arranged in anend-to-end relationship in a complete circle having a diameter longerthan several wave lengths, said conductors being spaced a short distanceabove a resistive dielectric, means connected to one end of each of saidconductors for energizing said conductors with a travelling wave andreflection preventing means connected between the other end of eachconductor and said resistive dielectric.

3. A broadcast antenna for vertically polarized radiation at low angleswith respect to ground comprising a number of conductors arranged in anend-to-end relationship in a complete circle,

said conductors being spaced a short distance above a resistivedielectric, means connected to one end of each of said conductors forenergizing said conductors with a travelling wave and refiectionpreventing means connected between the other end of each conductor andsaid resistive dielectric, said circle having a diameter of a number ofwavelengths at the operating frequency.

4. A broadcast antenna for vertically polarized radiation at low angleswith respect to ground. comprising a pair of conductors arranged in anend-to-end relationship in a complete circule having a diameter greaterthan several operating wave lengths, said conductors being spaced ashort distance above a high resistance dielectric, means connected toone pair of diametrically opposite ends of said conductors forenergizing said conductors with a travelling wave and reflection preventing means connected between the other end of each conductor and saidhigh resistance dielectric.

5. A broadcast antenna for radiating vertically polarized waves at lowangles with respect to a poorly conducting ground and comprising aconductor arranged around the circumference of a circle having adiameter of several wavelengths at the operating frequency, meansconnected to one end of said conductor for energizing said conductor andreflecting preventing means connected between the other end of saidconductor and ground.

6. A broadcast antenna for radiating vertically polarized waves at lowangles with respect to poorly conducting ground comprising a conductorarranged around the circumference of a circle having a diameter of theorder of several wavelengths at the operating frequency, means connectedto one end of said conductor for energizing said conductor andreflecting preventing means connected between the other end of saidconductor and said poorly conducting ground, said wire being spacedabove said poorly conducting ground a distance which is small comparedto a wavelength.

7. A broadcast antenna for radiating vertically polarized waves at lowangles with respect to a high resistance dielectric surface comprising aconductor arranged around the circumference of a circle having adiameter equal to several wavelengths at the operating frequency, meanscon nected to one end of said conductor for energizing said conductorand reflecting preventing means connected between the other end of saidconductor and said dielectic surface, the spacing between said wire andsaid surface being substantially less than a quarter wavelength at theoperating frequency. 7

NILS E. LINDENBLAD.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,381,089 Beverage June 7, 19212,247,743 Beverage July 1, 1941

